Electrooptical system



Aug. 6, 1935. F. GRAY ELECTROOPTICAL SYSTEM 3 Sheets-Sheet l ATTORNEYINVENTOR F GRAY Filed Jan. 10, 1931 Aug. 6, 1935. F. GRAY 2,010,543

ELECTROOPTICAL SYSTEM Filed Jan. 10, 1931 3 Sheets-Sheet 2 A TTORNEVAug. 6, 1935. F. GRA Y 2,010,543

ELECTROO-PTICAL SYSTEM Filed Jan. 10, 1931 3 Sheets-Sheet 3 FIG. 3

FIG. 4

IIIIIIIIII INVENTOR FGRAK BY ATTORNEY Patented Aug. 6, 1935ELECTROOPTICAL SYSTEM Frank Gray, New York, .N. Y., assignor. to BellTelephone Laboratories, Incorporated, 'New York, N. Y., a corporation ofNew York r Application January 10, 1931,, Serial No. 507,799

10 Claims. ((3-1. 178 6) This invention relates to electro-opticalsystems and more particularly to an image scanning mechanism. a 1

It has been proposed to use abelt provided with slots for projecting animage of successive unit lines of a field of view to be transmitted upona selenium plate and to scan the elemental areas of each illuminatedline by a commutating device, which comprises a pair of seleniumelements connected in series with each elemental area of the seleniumplate and a moving beam of light which simultaneously illuminates thepairs of elements'in succession, to releaseto a transmission circuitimage currents varying in amplitude with the tone values of thesuccessive ele mental areas'of the image. 7

.A system of the type just described possesses the disadvantage thatsel'enium presents a finite resistance whether illuminated or not; andit does not respond to rapid changes in light values. As a result,leakage current will flow through the circuit including theseleniumplate and commutator when a voltage is applied thereto even ifthe plate andcommutator are not illuminated, the system cannot beoperated at high speed, because of the lag of the selenium plate andcommutating elements, and the image currents will be distorted by theresidual resistance of the commutatorv elements when they areilluminated.

The present invention provides a scanning mechanism which operates in amanner similar to that described above, but which does not embody thedisadvantages hereinbefore noted. -An object'of the invention istoefiect high speed scanning in a system of the typedescribed above, byusing a commutating device comprising light sensitive. devices activatedby a beam of lightof constant intensity.

Another object is to produce undistorted image currents. g i j fAnadditional object is to;prevent theflow of leakage currents. g Inaccordance with one embodiment of the invention, an image of a subject,or field of view, ispro'jected upon a ,group of photoelectric cells eachof which is connected in series with another photoelectric cell. Theseries-connected cells are arranged to constitute a second group, whichare Ysuccessively illuminated by a beam of light of constant intensityto release image currents, producedinthe respective cells of the firstgroup, to ,a communicating channel. j The second group consists ofphotoelectric .cells, each having a current carrying capacity which isgreater than the maximum currentcaused by the activation any cell ofthefirst group. a

An image maybe projected upon a bank .of photoelectric cellsconstituting alcomplete image field,'or successive lines of the imagemaybe 5 caused to traverse a row of cellslcorresponding to a'unit lineof the image. V I? A description of the invention follows and isillustrated in the attached drawings, inwhich i Fig. 1 diagrammaticallyillustrates a system embodying the invention; J 1

Fig. 2 illustrates a difierentform of scanning means which may be usedin place of that shown in Fig. If and Figs. 3'and 4 show scan'ning meanswhich may 15 be substituted'for that of Fig. 2.

u Referring to Fig. 1, there is shown a subject or field of view i, alens 2 for projecting animage of the subjectupon'photoelectric cells 3correspending in numberto the-elemental areas of 0 the image andarranged to constitute a bank} of rectangular form, and a second setofphoto electric cells 5, which correspondv in number to those of the bank4. Cells 5" are of such character that no current flows between theirelectrodes when they are dark, i. e., when they are not'illuminated, andare of such current carrying capacity that, when illuminated by a. beamof light of predetermined constant intensity, they are activated tocause the production of a current 36 greater than the largest currentever produced .by any cell a or the first bank when illuminated by animage of the field of view.' Each of the cells 5 is connected in serieswith one of the cells 3 and through a common circuit to fan 35 amplifier6 included in a transmission circuit 1.

A source of light 8 cooperates with an optical system including lens 9;a rotating disc l0 provided with a row of apertures l l arrangedin aspiral lineQand a lens 12 to produceia moving 40 beam of light of thedesired/constant intensity which successively illuminates the cells 5which are thereby renderedconductiva flmag "currents, corresponding inamplitude to the tone l4 over which transmission is effected to areceiving station.

At the receiving station, the incoming image currents are amplified inthe device [5 and applied toglow lamp l6 associated with a rotating discI! provided with a row of apertures I8 arranged in a spiral line. Inaccordance with more or less standard practice, the lamp and disccooperate to produce an image which may be directly viewed by anobserver 0 or may be projected by a suitable optical system on a screenfor audience viewing.

To permit production of the image, the disc and I1, driven by the motorsl9 and 20, must operate in synchronism and in phase with each other andare driven at such a rate that a complete image field is scanned and animage thereof is produced during each complete revolution thereof andwithin the period of persistence of vision. A suitable system which maybe used to maintain synchronous operation of the discs 10 and I1 isdisclosed in U. S. Patent 1,999,376 of H. M. Stollenissued April 30,1935. Lamp 16 may be of any suitable type adapted to supply lightvarying in accordance with the amplitudes of the incoming imagecurrents, for example, it may be a glow lamp of the type disclosed in U.S. Patent 1,918,309 of H. W. Weinhart, issued July 18, 1933.

The apparatus of Fig. 2 comprises a lens 2| for producing an image of afield of view in the plane of disc 22 provided with slots 23 whichsuccessively sweep across a series of photoelectric cells 2 1 each equalin length to a unit line of the image. Cells 24 are each connected inseries with a photoelectric cell 25 having a current carrying capacitygreater than the maximum current produced by any of the cells 24.

As described in connection with Fig. 1, the cells 25 are non-conductivein the dark, and they are traversed by a moving beam of light of thedesired constant intensity to activate them by the optical system 8, 9,l0 and l 2, whereby image currents corresponding in amplitude tosuccessive elemental areas of the image are released to the amplifier 6.The image is completely scanned during each revolution of the disc I0and it is driven by a motor activating the disc 22 to which it iscoupled by a gear, indicated at 50, to cause the beam of light to beswept across cells 25 at such a rate that complete scannings occurwithin the period of persistence of vision. The gearing 50 is of suchratio that the disc I0 is operated at the proper relative speed withrespect to the disc 22.

Fig. 3 illustrates a disc 26 provided with a series of lenses whichserve to move an image of a field of view across a stationary slot 21provided in a screen or mask 28 having associated therewith a row ofphotoelectric cells 29, corresponding in number to the unit lines of theimage. Connected in series with each of the cells 29 is a cell 30whichis non-conductive in the dark. Cells 30 are adapted to beilluminated in succession as described above by a movable beam of lightof the desired constant intensity supplied through the optical system 8,9, l8 and [2. As the disc 26 rotates, light from successive unit linesof the image illuminates the cells 29, which are thereby activated tocause the production of image currents corresponding in amplitude to thetone values of elemental areas of the lines. The disc I0 is rotated andthe beam of light sweeps across cells 30 at such a rate that imagecurrents cor responding to elemental areas of the complete field of vieware released to the amplifier 6 within the period of persistence ofvision. The gear 50 serves tocouple the motor to the disc I0 so that itis rotated at the desired speed with respect to the disc 26.

As shown in Fig. 4, the lensed disc 26 of Fig. 3 may be replaced by asystem of rotating mirrors 3! to sweep successive unit lines of theimage across the stationary slot 21. The gearing 5| serves to couple thedriving motor for the mirror system to the disc iii, which is therebyrotated at the desired rate relatively to the mirrors.

If desired, a pair of rotating prisms could be used, as disclosed in U.S. Patent 1,647,631 of H. E. Ives, dated November 1, 1927, to causelight derived from successive elemental areas of the image to illuminatecorresponding photoelectric cells 3 of the first group of Fig. 1 whilethose of the second group 5 are successively illuminated by a movingbeam of light of the desired constant intensity provided by the opticalsystem 8, 9, l0 and I2, to release image currents, corresponding to thecomplete field, to the amplifier 6 at a rate within the period ofpersistence of vision.

In the apparatus of Figs. 2 to 4, the traversal of the movable beam oflight should be controlled by the disc ID to operate in synchronism andin phase with the disc I? at the receiving station. The synchronizingsystem disclosed in the above mentioned Stoller application may be usedfor this purpose.

One advantage of the present system is that it reduces the speed ofmoving parts and hence permits'large images to be scanned at high speed,Without causing the flow of leakage currents and without distortion ofthe image currents supplied to the transmission circuit. As a resultlarge aperture lenses can be used to effect 2. corresponding gain in theamount of light available to produce image currents.

What is claimed is:

1. A television system comprising a group of photoelectric cells, asecond group of photoelectric cells each of greater current carryingcapacity than those of the first group and respectively connected inseries with a cell of the first group, means for projecting an image ofa field of view upon said first group of cells, and means forsuccessively activating the cells of the second group.

2. A television system comprising a group of photoelectric cells, asecond group of photoelectric cellseach of greater current carryingcapacity than those of the first group and respectively connected inseries with a cell of the first group, means for projecting an image ofa field of view upon said first group of cells, and means for producinga moving beam of light of constant intensity for successively activatingthe cells of the second group.

3. A television system comprising light sensitive devices, means forprojecting an image of a field of View upon said devices, other lightsensitive devices each connected in series with one of said firstmentioned devices and of greater current carrying capacity than thedevice with which it is connected, and means for successively activatingsaid other devices.

4. A photoelectric cell assembly for use in a television systemcomprising a bank of photoelectric cells, the number of cells beingequal and their arrangement similar to the desired number andarrangement of elemental areas in a field of view, and a group ofphotoelectric cells equal in number to those in said bank of cells, eachcell of said group having greater current carrying capacity than thecells of said bank and each respectively connected in series with a cellof said bank.

5. A television system compring a bank of photoelectric cells, thenumber of cells being equal and their arrangement similar to the desirednumber and arrangement of elemental areas in a field of view, a group ofphotoelectric cells equal in number to those in said bank of cells, eachcell of said group having greater current carrying capacity than thecells of said bank and each respectively connected in series with a cellof said bank, means to illuminate each cell of said bank with light fromthe corresponding elemental area of the field of view, and means tosuccessively activate the cells of said group of cells, each cell beingactivated while the corresponding cell of the bank is illuminated;

6. A television system comprising a, bank of photoelectric cells, thenumber of cells being equal and their arrangement similar to the desirednumber and arrangement of elemental areas in a field of view, a group ofphotoelectric cells equal in number to those in said bank of cells, eachcell of said group having greater current carrying capacity than thecells of said bank and each respectively connected in series with a cellof said bank, and means to successively illuminate the cells of saidgroup with a moving beam of light of constant intensity.

'7. A television system comprising a plurality of elongatedphotoelectric cells equal in number to the elemental lines of a field ofview, means to simultaneously illuminate an elemental portion only ofeach of said cells, which. portions correspond to elemental areas ofsaid elemental lines, a second group of photoelectric cells equal to thenumber of elongated cells, each cell of this group having a currentcarrying capacity greater than the maximum current produced by any ofsaid elongated cells and each respectively connected in series with oneof said elongated cells, and means for successively activating the cellsof said second group.

8. An electro-optical system comprising two cellular structures eachhaving the same number of compartments, a photoelectric cell positionedin each compartment each of said cells having two electrodes one acathode and the other an anode, a connection common to all of theelectrodes of one kind of the cells in one structure, another connectioncommon to all of the electrodes of the other kind of the cells in theother structure, conductors individual to pairs of cells one of which isin each structure, each said con-- ductor joining the not commonlyconnected electrodes of the said pairs of cells, a source of currentenergizing said cells through said common connections, and means toenergize the cells of one structure in succession with an energycarrying beam.

9. An electro-optical system comprising two cellular structures eachhaving the same number of compartments, a photoelectric cell positionedin each compartment each of said cells having two electrodes one acathode and the other an anode, a connection common to all of theelectrodes of one kind of the cells in one structure, another connectioncommon to all of the electrodes of the other kind of the cells in theother structure, metallic conductors individual to pairs of cells one ofwhich is in each structure, each said conductor joining the not commonlyconnected electrodes of the said pairs of cells, a source of currentenergizing said cells through said common connections, and means to energize the cells of one structure in succession with a moving beam oflight.

10. An electro-optical system comprising two cellular structures eachhaving the same number of compartments, a photoelectric cell positionedin eachrcompartment each of said cells having two electrodes one acathode and the other an anode. a connection common to all of theelectrodes of one kind of the cells in one structure, another connectioncommon to all of the electrodes of the other kind of the cells in theother structure, conductors individual to pairs of cells one of which isin each structure, each conductor joining the not commonly connectedelectrodes of the said pairs of cells, a source of current energizingsaid cells through said common connections, and means to energize thecells of one structure in succession with an energy carrying beam, thecells in the successively energized structure each having a greatercurrent, carrying capacity than the corresponding cell in the otherstructure.

FRANK GRAY.

